The words liquor and liqueur are so similar, it is easy to confuse the two. And although both liquors and liqueurs contain alcohol and are crucial ingredients in our favorite cocktails, the terms are not interchangeable. In general, liquor is not sweet while liqueurs are and are used as flavoring agents in mixed drinks. However, many liquors are available in flavored forms nowadays, which just adds to the confusion.
Liquor, also known as spirits, is an alcoholic beverage--such as gin, vodka, tequila, and rum--made of grains or other plants which are fermented into a potent drink. The distillation process which occurs after fermenting separates the water from the alcohol, increasing the alcohol content to at least 20 percent (vodka generally has 40 percent).
Although sugar is generally used in the fermentation process, the resulting liquor is not sugary sweet. And even though liquors are available today in flavored forms (such as citrus and cinnamon), they are not sweet to the palate. The flavor is usually added after distilling through a steeping process, much like how vinegar and oils are infused.
In general, liqueurs are sweetened spirits with various flavors, oils, and extracts. Rum, whiskey, brandy and other liquors can serve as a base spirit for liqueurs. Liqueur alcohol content can range from a low 15 percent (30 proof) to 55 percent (110 proof), so potency is not a distinguishing factor.
Our ancestors referred to liqueurs as cordials, and they were often used medicinally.
Liqueurs can range greatly, from coffee to almond to orange flavors. There are also cream liqueurs which have cream added, and créme liqueurs which are much sweeter likened to a potent syrup. Grand Marnier® is a delicious example of an orange liqueur which is an ingredient in classic cocktails such as tequila sunrise and makes a flavorful addition to many recipes.